NMDARs are ionotropic glutamate receptors widely expressed in the CNS, where they mediate phenomena as diverse as neurotransmission, information processing, synaptogenesis, and cellular toxicity. They function as glutamate-gated Ca²⁺-permeable channels, which require glycine as coagonist, and can be modulated by many diffusible ligands and cellular cues, including mechanical stimuli. Previously, we found that, in cultured astrocytes, shear stress initiates NMDAR-mediated Ca²⁺ entry in the absence of added agonists, suggesting that more than being mechanosensitive, NMDARs may be mechanically activated. Here, we used controlled expression of rat recombinant receptors and noninvasive on-cell single-channel current recordings to show that mild membrane stretch can substitute for the neurotransmitter glutamate in gating NMDAR currents. Notably, stretch-activated currents maintained the hallmark features of the glutamate-gated currents, including glycine-requirement, large unitary conductance, high Ca²⁺ permeability, and voltage-dependent Mg²⁺ blockade. Further, we found that the stretch-gated current required the receptor's intracellular domain. Our results are consistent with the hypothesis that mechanical forces can gate endogenous NMDAR currents even in the absence of synaptic glutamate release, which has important implications for understanding mechanotransduction and the physiological and pathologic effects of mechanical forces on cells of the CNS.

SIGNIFICANCE STATEMENT We show that, in addition to enhancing currents elicited with low agonist concentrations, membrane stretch can gate NMDARs in the absence of the neurotransmitter glutamate. Stretch-gated currents have the principal hallmarks of the glutamate-gated currents, including requirement for glycine, large Na⁺ conductance, high Ca²⁺ permeability, and voltage-dependent Mg²⁺ block. Therefore, results suggest that mechanical forces can initiate cellular processes presently attributed to glutamatergic neurotransmission, such as synaptic plasticity and cytotoxicity. Given the ubiquitous presence of mechanical forces in the CNS, this discovery identifies NMDARs as possibly important mechanotransducers during development and across the lifespan, and during pathologic processes, such as those associated with traumatic brain injuries, shaken infant syndrome, and chronic traumatic encephalopathy.

NMDAR 是在 CNS 中广泛表达的离子型谷氨酸受体，它们在其中介导神经传递、信息处理、突触发生和细胞毒性等多种现象。它们起到谷氨酸门控 Ca ²⁺渗透通道的作用，需要甘氨酸作为共激动剂，并且可以通过许多可扩散的配体和细胞信号（包括机械刺激）进行调节。以前，我们发现，在培养的星形胶质细胞中，剪切应力会引发 NMDAR 介导的 Ca ²⁺在没有添加激动剂的情况下进入，这表明 NMDAR 不仅具有机械敏感性，还可能被机械激活。在这里，我们使用大鼠重组受体的受控表达和非侵入性的细胞单通道电流记录来表明温和的膜拉伸可以替代神经递质谷氨酸在门控 NMDAR 电流中。值得注意的是，拉伸激活电流保持了谷氨酸门控电流的标志性特征，包括甘氨酸需求、大的单一电导、高 Ca ²⁺渗透性和电压依赖性 Mg ²⁺封锁。此外，我们发现拉伸门控电流需要受体的细胞内结构域。我们的结果与以下假设一致，即即使在没有突触谷氨酸释放的情况下，机械力也可以控制内源性 NMDAR 电流，这对于理解机械力转导和机械力对中枢神经系统细胞的生理和病理影响具有重要意义。

意义声明我们表明，除了增强低激动剂浓度引起的电流外，膜拉伸可以在没有神经递质谷氨酸盐的情况下控制 NMDAR。拉伸门控电流具有谷氨酸门控电流的主要特征，包括对甘氨酸的要求、大的 Na ⁺电导、高 Ca ²⁺渗透性和电压依赖性 Mg ²⁺堵塞。因此，结果表明，机械力可以启动目前归因于谷氨酸能神经传递的细胞过程，例如突触可塑性和细胞毒性。鉴于中枢神经系统中普遍存在机械力，这一发现将 NMDAR 确定为在发育和整个生命周期以及病理过程中可能是重要的机械传感器，例如与创伤性脑损伤、婴儿摇晃综合征和慢性创伤性脑病相关的那些过程。